1. Field of the Invention
The present invention relates generally to RF circuits, and particularly to RF circuits and shielding structures.
2. Technical Background
Referring to FIG. 1, a cross-sectional view of a stylized conventional microstrip circuit 10 is depicted. The microstrip circuit 10 includes a dielectric layer 14 having microstrip layer 16 disposed on the top of the dielectric layer 14. A metallized ground layer 12 is disposed on the underside of the dielectric layer 14. As those of ordinary skill in the art will appreciate, the microstrip circuit 10 may be employed to implement distributed element filters. Stated differently, as the operating frequency increases, lumped elements become impractical and filter components are realized with transmission line components (i.e., distributed elements). The metallized layers (12, 16) may be implemented using any suitable materials such as copper, gold, silver, etc. The dielectric layer 14 may also be implemented using any suitable material such as FR-4, alumina, etc.
One drawback associated with the microstrip network 10 relates to its ability to propagate electromagnetic signals into the surrounding RF environment. The electromagnetic signals emanating from the microstrip network 10, for example, can be unintentionally received and conducted by other networks operating in the same environment and thus interfere with these networks. Thus, the signals generated by the microstrip lines would be interpreted as noise or interference signals. Moreover, in a system that employs multiple microstrip circuits in close proximity to each other, cross-coupling of the electromagnetic signal may occur, resulting in cross-talk between adjacent microstrip transmission lines.
In reference to FIG. 2, a cross-sectional view of the circuit depicted in FIG. 1 with a conventional shielding structure 18 is shown. Thus, in one approach that has been considered, multiple microstrip filters may be disposed adjacent to each other in an array on the same plane with some type of shielding structure disposed therebetween. (For clarity and simplicity of illustration, only one microstrip network 10 is shown in FIG. 2). One drawback to this approach is that it is not spatially efficient in terms of the overall footprint because it requires multiple microstrip networks 10 disposed side-by-side and adjacent to each other (As implied by FIG. 2). Stated differently, this approach often requires a large surface area and is thus not suitable for miniaturized applications. This approach is also often unpractical for highly integrated applications for the same reasons.
In another approach that has been considered, stripline filters have been employed in multi-layered structures to reduce the footprint and achieve a higher degree of integration. One drawback to this approach is that often, an entire set of filters has to be designed and manufactured at the same time and lack modularity. Moreover, stripline technology often has a limited pool of material choices and may present increased manufacturing uncertainties relative to simpler technologies due to the characteristics of the specific bonding processes used in stripline technology. For example, comparable microstrip circuits do not have such limitations and are thus relatively inexpensive when compared to stripline circuits.
What is needed, therefore, is an integrated support and shielding structure that can be used in conjunction with a plurality of microstrip circuits without interference, cross-talk or any of the other drawbacks described above.